This invention relates to a method and apparatus for measuring the thickness of an object to be measured with high precision in a non-contact manner, and particularly to a plate thickness measuring method and apparatus suitable for measuring an extremely thin plate of any material.
In semiconductor manufacturing processes, it is important to produce constant-thickness wafers for uniform characteristics. For example, a wafer for pressure sensor diaphragms, which is etched into a thin film, an extremely thin metal foil or plate, and the like have been measured in their thickness by a dial gauge of the contact type. In this case, the measurement has been made at several points on the plate to be measured, and the thickness of the other parts is assumed from the measured values at the several points. However, in this conventional measuring method, since the measuring probe is made to contact with the object to be measured, the object to be measured may become flawed or contaminated by the contacting operation, and this becomes defective. Moreover, the measured thickness is dependent on the contact pressure of the measuring probe and the measuring point, and thus sufficient precision (less than 1 .mu.m) can not be obtained.